Last week, in the wake of Hurricane Sandy, readers @amyh914, @dauentina and ‏@TheRealYadiM all asked if we should expect a spike in birth rates along the East Coat nine months from now — a mini-baby boom caused by Sandy.

The idea that disasters and birth rates are correlated goes back at least to at least 1965, when a blackout plunged New York City into darkness for several hours one November night.

The following August, the New York Times noted a “sharp increase in births” in several of the city’s large hospitals, proclaiming in a headline “BIRTHS UP 9 MONTHS AFTER THE BLACKOUT.”

It seems plausible enough. TVs and telephones weren’t working, and the subway wasn’t running — what else were people going to do with their time but get it on? After many disasters since then, we’ve heard the same folk wisdom. “It is evidently pleasing to many people,” said Richard Udry, a sociologist at the University of North Carolina who studied post-blackout birth rates, “to fantasize that when people are trapped by some immobilizing event which deprives them of their usual activities, most will turn to copulation.”

The Evidence For … and Against

The actual evidence for hurricane/snow/tornado/whatever babies is mixed. A few studies have found that natural and man-made disasters can influence the birth rate and others haven’t. When disasters do come into play, the birth rate doesn’t always increase; the catalyst for conception is sometimes boredom and sometimes something more complicated.

Udry’s study found that the blackout babies of 1966 were nothing special. In 1970, he looked at NYC births over a several-year period and couldn’t find a statistically significant spike in births associated with the blackout. The number of babies born within the time frame where the day of the blackout could have been the date of conception was “not at all remarkable for 1966 when compared to the previous five years.”

In 2002, Catherine Cohan and Steve Cole, human development and family studies researchers at Penn State University, examined 22 years’ worth of marriage, birth and divorce rates from South Carolina. They found that in 1990—the year after Hurricane Hugo struck and caused about $5.9 billion in property damage in the state, killed 35 people and left 50,000 homeless — marriage, birth and divorce rates all shot up in the counties that were declared disaster areas.

With all three moving in the same direction, Cohan and Cole concluded that the stress and life-threatening danger from the storm provoked “significant and relatively quick action in [people’s] personal lives that altered their life course.”

In 2005, three psychologists from the University of Oklahoma wondered if the fear and stress caused by a man-made disaster might have a similar effect. They looked at birth data from Oklahoma City and its surrounding counties for the years 1990 to 1999—about five years of data before the 1995 Oklahoma City bombing would have any effect on births, and about four years of data afterward—and found a strong increase in birth rates in and around the city nine months after the bombing.

They thought that the increase happened either because people felt a threat to their own sense of mortality or considered the fragility of life after the bombing, and responded by strengthening their family.

Blame It On The Weather

For a 2010 study, economists from the U.S., Germany and China analyzed birth data and hurricane and tropical storm advisories in 47 counties along the United States’ Gulf and Atlantic Coasts from 1995 to 2001. They found that “low-severity” advisories correlated positively with birth rates nine months later and that “high-severity” advisories correlated negatively. Areas that experienced tropical storm or hurricane watches had a post-storm baby boom, but areas that had storm or hurricane warnings saw a decrease in births.

According to NOAA, watches mean the possibility of a storm and usually come approximately 48 hours in advance of it. During a watch, people should prepare their homes and then remain in them. A storm warning means a storm should be expected, and usually come about 36 hours in advance. In the event of a warning, people should finish storm preparations and be ready to evacuate.

The differing birth rates following the two events, the researchers reason, is tied to the perceived danger of the event and the things people do during them. During a storm warning, people might stock up on food and hunker down in the house. After a while, they might get bored watching TV, or maybe the power goes out, and they head to the bedroom—in line with the popular prediction. In a more severe warning, though, people might more concerned with gathering supplies, securing their homes and getting ready to leave the area. Even if they’re riding the storm out at home, the researchers think, they may be too worried or occupied to engage in romance.

So, will we see a lot of babies named Sandy next summer? Maybe, but certainly not in all areas and not always because of the exact same reasons. The ties between catastrophe and conception are more complex than we might think.